The invention relates generally to power supply systems and more specifically to a system and method for a power converter to supply fault currents without over-rating.
Many devices, such as power supply systems, operate on power drawn from generators. The generator, in turn, draws power from systems such as wind turbines, gas or diesel-driven engines, turbines, or any other suitable drive system. Converter systems are usually designed to draw power from the generator and to provide the power either to a fixed frequency power grid or at a desired frequency to various loads. In other applications, such as motors, power converters are designed to draw power from a grid and provide the power to the motor.
In some applications, when there is a failure at the load, the converter systems are required to provide fault currents to the load for several cycles of the fundamental voltage. Typically, the fault current is of relatively high value. The fault current is provided to ensure the timely protection of the load. In most power electronic applications, the time interval required by the protection system to respond amounts to steady state operation for the power electronic equipment.
In order to withstand high fault current, such converters are often over-rated. Over-rating the converter system results in bulky and oversized converter systems due to larger size of devices and thermal management system, passive components like dc-link capacitors and filter inductors. In addition, the increase in components also results in an increase in the cost of the converter system.
Another requirement of converter systems is to comply with standards of harmonic injections or perturbations to the system to which power is applied (e.g. a power grid). The switching frequency of most converter systems is limited to a few hundred hertz, resulting large harmonic distortion. The harmonic distortion can be corrected by using a filter comprising large passive components. However, this again results in making the converter system bulky and heavy.
Therefore, there is a need to design a compact and cost effective converter system for withstanding high fault currents during fault conditions and effectively filtering harmonic components.